Beat the eggs into a bowl for 30-60 seconds together with salt and pepper.
In the same bowl, add sliced mushrooms, chopped leeks, bell pepper and olives.
Mix everything with a fork until combined with beaten eggs.
Preheat the cast iron skillet and throw in the butter. Keep the heat to medium temp since we don’t want to burn the butter or the eggs.
Once butter is almost melted, slowly pour eggs mixture into skillet.
Cook gently on medium heat until the eggs are almost done. Use a thin spatula and go under the eggs to prevent sticking.
When eggs are almost cooked, add baby spinach leaves on top and cook for 1 more minute.
Remove the skillet from heat and set aside to cool down for 1-2 minutes.
Transfer to a plate and separate into desired portions. Enjoy!